Pros and cons of server consolidation

Fewer servers can help to reduce IT costs, but there are a number of potential pitfalls.

Figures from analyst Gartner show that many firms are now consolidating onto a smaller number of servers.

In 1998, 30 per cent of enterprises were consolidating servers, 45 per cent were considering consolidation, and 25 per cent had no plans to consolidate at all. Last year these figures had shifted to 69, 25 and six respectively.

Often consolidation involves moving software from multiple distributed servers onto partitioned mainframes or clusters of PC servers. However, server consolidation has its own pitfalls.

For example, a common consequence of distributed systems is that firms end up with a collection of different server platforms fulfilling different functions, something which is difficult to manage, according to Gartner vice president John Phelps.

"[Consolidation is an attractive option because otherwise] adding a single application typically adds three to five servers to the data centre for such things as production, development, testing and backup," he said.

"Many such servers run at very low levels of utilisation. We have found examples where the utilisation is as low as five per cent, and 15 to 25 per cent is quite typical."

Logical, physical or rationalised?

Phelps identified three categories of consolidation. Logical consolidation is where there is no physical relocation of servers, simply a logical coming together through the use of common processes and standard systems management procedures across the applications.

Physical consolidation is the server farm approach, co-locating servers in as few places as possible. Rationalised consolidation is the traditional IBM mainframe approach, using partitioning and workload management tools on extremely powerful servers to implement the applications previously run on many smaller machines.

Phelps pointed out that all of these approaches can potentially reduce costs and improve manageability, but warned that they also present pitfalls for the unwary.

Rationalised consolidation has the longest history, and is typically used to consolidate similar applications, such as web servers, file servers and database applications.

But there are very few applications that require all the power of a 16- or 32-way server, so technology for dividing such servers into smaller, more manageable units is required, such as workload management tools. "[But] workload management for consolidation of different database managers is still very difficult," said Phelps.

Another worry for IT managers is the cost of software following consolidation. "Consolidating can mean moving an application from a four-processor server to a 32-processor unit," he explained.

"But once a vendor knows that a user is running an application on a larger system, they can charge more. That is why I am suggesting that users consider consolidating applications from the same vendor [to achieve a stronger bargaining position].

"It then becomes important to ensure that the applications do not have peak loads at the same time, otherwise an even bigger system will be required, with lower average levels of utilisation."

No quick answer

The real problem for firms is that, although consolidation is becoming more popular, there are no easy solutions.

"Server consolidation is not a simple task," Phelps wrote in a Gartner report. "Unfortunately, it is not possible to buy off-the-shelf server consolidation solutions despite the claims made in vendor marketing brochures."

The goal is to build workload management systems that run a single copy of an operating system across the consolidated environment, capable of running multiple applications in dynamically resizeable partitions, said Phelps. In the old mainframe world this capability is normal.

IBM offers its zSeries OS/390 systems for this purpose. Companies can use a zSeries system as a dynamically partitioned, virtual server farm. However, in the distributed Unix and Windows world, this type of capability is only just starting to appear.

SUMMARY